1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to methods and apparatus for stacking multiple semiconductor devices and packaging the same.
2. Description of the Related Art
Some time ago semiconductor chip designers began stacking multiple semiconductor dice (aka “dies”) vertically in order to obtain more functionality without an attendant increase in required package substrate or circuit board area. A variety of techniques have been used to electrically connect adjacent dice in such stacked arrangements. One technique has involved the use of wire bonds leading from contact pads on one die to corresponding contact pads on an adjacent die. Another technique that has been introduced more recently involves the use of so-called thru-silicon-vias (TSV). A typical TSV is a conductive via that extends nearly or perhaps entirely through a semiconductor chip, depending on the presence or absence of any intervening conductor pads at one or the other of the principal surfaces of the chip.
Most semiconductor chips are eventually mounted to some form of circuit board or enclosure. Typical examples include semiconductor chip package substrates, circuit cards, motherboards and other types of packaging closures. A technical challenge associated with most mounting schemes is the establishment of electrical interfaces between the semiconductor die or dice and the receiving circuit board. The fabrication of these electrical interfaces may be particularly challenging in a stacked dice arrangement. This follows from the fact that the multiple semiconductor chips may, by definition, include a significantly higher number of input outputs than a single semiconductor device.
One conventional technique for establishing electrical interconnects between a stacked dice arrangement and a circuit board involves the use of wire bond interconnects. Plural wire bonds are connected to conductor pads on one or more of the dice in the stacked dice arrangement and also to corresponding conductor pads on the circuit board or some other device on the circuit board. Another conventional arrangement for connecting a stacked dice arrangement to a circuit board involves the use of some form of control collapse bump arrangement wherein the plural solder joints are established between a lowermost of the stacked dice and the circuit board. This typically entails the formation of a solder bump on the lowermost die and a corresponding solder bump on the circuit board followed by a solder reflow process.
A more recent innovation involves the use of copper pillars that project outwardly from the lowermost die of a stacked dice arrangement and interconnect electrically with a circuit board. This conventional arrangement utilizes a low profile solder paste placed in plural low-profile openings in a solder mask on the circuit board. The lower ends of each of the copper pillars is fitted with a small solder cap. To establish the requisite connections, the die is positioned so that the solder caps of the copper pillars are in proximity or in contact with the low profile solder paste portions and a reflow process is performed. Expenses in the form of material and labor costs are associated with the conventional copper pillar process.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.